Motor protection for a powered door system

Abstract

A motor protection circuit for an electric motor driven by a pulse width modulated amplifier. It has a capacitor and a first conduction path connected to a first terminal of the capacitor and connectable to a first conductor. It also has a second conduction path connected to the second capacitor terminal and connectable to a second conductor. There is a DC voltage difference between the first conductor and the second conductor. There is a third conduction path between the first terminal and the second terminal. The third conduction path having a resistance which is lower than the resistance of the first conduction path plus the resistance of the second conduction path. The third conduction path passes through a switch which has an input connection to be opened and closed thereby. The input connection is for receiving a signal indicating a motor overload condition, whereby the capacitor discharge switch is closed when the signal indicates the motor overload condition and the capacitor discharge switch is opened when the signal does not indicate the motor overload condition. A charge on the capacitor increases when the signal does not indicate the motor overload condition and the charge on the capacitor decreases when the signal indicates the motor overload condition. The circuit also has a voltage comparator receiving the voltage of the capacitor. The voltage comparator produces a signal for shutting down the motor.

Description

The present invention relates, in general, to motor protection circuits and, more particularly, the instant invention relates to motor protection for transit vehicle door systems and / or elevator doors.Powered door systems for use on transit vehicles, elevators and the like typically experience very heavy usage which may place severe demands on the motors that open and close the doors. Such motors are generally undersized due to size and weight constraints. Consequently, motor protection circuits are generally necessary to prevent burn out of such motors.The friction which the doors experience when they are moved between open and closed positions may increase due to a number of factors including temperature, loss of lubricant, galling of load bearing surfaces, etc. In such applications, the doors may be quite massive and may be required to move rapidly between open and closed positions. This places a heavy demand on the motors to overcome the inertia of the doors when accelerating an...

Images